Solution: Calculate the Number of Nodes in a Graph Level

def number_of_nodes(my_graph, level):
    """
    Calculates the number of nodes at given level
    :param graph: The graph
    :return: Total number of nodes at given level
    """
    source = 0
    # Mark all the vertices as not visited
    visited = [0] * (len(my_graph.graph))
    # Create a queue 
    queue = []
    # Result string
    result = ""
    # Mark the source node as
    # visited and enqueue it
    queue.append(source)
    visited[source] = 1
    while queue:
        # Dequeue a vertex from queue
        source = queue.pop(0)
        # Get all adjacent vertices of the
        # dequeued vertex source. If a adjacent
        # has not been visited, then mark it
        # visited and enqueue it
        while my_graph.graph[source] is not None:
            data = my_graph.graph[source].vertex
            if visited[data] == 0:
                queue.append(data)
                visited[data] = visited[source] + 1
            my_graph.graph[source] = my_graph.graph[source].next
    # Counting number of nodes at given level
    result = 0
    for i in range(len(my_graph.graph)):
        if visited[i] == level:
            result += 1
    return result
# Main to test above function
if __name__ == "__main__":
    V = 5
    g = Graph(V)
    g.add_edge(0, 1)
    g.add_edge(0, 2)
    g.add_edge(1, 3)
    g.add_edge(1, 4)
    print(number_of_nodes(g, 2))